Aseptic packages refer to sealed containers containing a substantially uniform predetermined amount of a product made in accordance with commercial aseptic packaging standards. Commercial aseptic packaging involves introducing a sterile product into a sterile container and then hermetically sealing the container in an environment substantially free of microorganisms capable of growing in a shelf stable product at temperatures at which the cooled finished product is likely to be stored during distribution and storage prior to consumption. Hermetically sealed containers minimize the transmission of any gas or fluid through the container package so that there is substantially no biological transmission. Preferably, the package is also substantially free of air which, if present in significant amounts, could promote undesired microbial growth or, even in the absence of microbial growth, adversely affect the taste or color of a product. Typical products are fluent materials, specifically, a fluid drink such as pasturized milk, fruit juices, and the like.
The sterile containers commonly comprise a laminated web packaging material preferably having at least one layer of current carrying material such as aluminum foil, an exterior layer of thermoplastic material to become the package interior in contact with the product, and an exterior layer of material for contact with the environment. The laminated material, also referred to herein as "polyfoil web", is typically strong enough to stand upright in a somewhat rigid finished configuration to contain the product for shipping and storage, and commonly includes a conventional paperboard structural layer. Product labeling and registration marks and the like may be printed on the paperboard layer or the outer thermoplastic layer. In the invention described below, the most preferred polyfoil web to use comprises a laminate of, in order, a layer of low density polyethylene, paper stock, Surlyn.RTM., aluminum foil, Surlyn.RTM., and linear low density polyethylene. The low density polyethylene could also be a high density polyethylene, and the linear low density polyethylene layer could be a low density polyethylene.
The thermoplastic material forming the package interior must be capable of being sealed together to form hermetic seals. Typically, opposing thermoplastic layers are heated to a melting temperature so that they will fuse together. The thermoplastic and metallic foil layers act in concert to provide the hermetic barrier for the aseptic package. The metallic foil layer provides a light and oxygen barrier. The outer layer is commonly a thermoplastic material that can be heated so that the package seams and triangular tabs of excess material formed during final forming or bricking of the packages can be flattened or tacked against the package sidewalls to form an aesthetically pleasing package.
Such polyfoil laminates may include spaced access means to enable the user to readily extract the product from the finished package.
Several methods and machines for forming aseptic and non aseptic packages or cartons from paper stock and laminated web materials are known. These methods and machines generally fall into two categories, blank fed and continuous web fed.
In blank fed machines, the supply of web first is separately formed into cut and scored blanks. The blanks are then fed into the forming section of the machine one at a time and erected into containers. Many machines operate on several blanks at different stages of construction at a time. For aseptic packaging, the containers are sterilized, filled with a sterile product, and hermetically sealed closed while in a sterile environment. The seams of these containers are typically formed by gluing or heat pressing overlapping flaps together.
Some blank fed machines form the blanks into cartons intermittently, performing one assembly operation on the blank or carton at each station and advancing the blank or carton from station to station. Other blank fed machines operate semi-continuously by continuously advancing the blank to form the container and then intermittently advancing the container to sterilize, fill, and seal the container. One commercial intermittent type blank fed aseptic machine is Combiblok, Model No. CF 606A.
In continuous web fed machines, the web is taken directly off the roll of web stock, scored (unless prescored on the roll), and fed into the machine. The machine then folds the web to form a column, seals the longitudinal edge to form a tube, fills the tube with a product, and clamps, seals, and severs the tube to form the packages. The web advance may be continuous, to gradually manipulate the web into sealed packages, or intermittent, to perform each assembly operation while the web is stationary or while the web is moving between stations. The sealing steps typically involve thermally sealing thermoplastic materials together to form an hermetic seal. Thermal sealing is brought about by using, for example, radiant heat, heated contacting members, or induction heating coils (for webs having a conductive layer integrated therein or applied thereon).
For aseptic packaging, the web is sterilized and fed into a sterile machine section, so that the tube is sterile and the package is formed, filled and sealed in a sterile environment. One commercial automatic continuous feed aseptic machine is Tetra-Pak Model AB 9. Other known aseptic machines include International Paper Co.'s web fed aseptic package machine, Model SA.
In many of the machines, reciprocating means are used to operate on the web either when the web or package is stationary, reciprocating into position and operation and then reciprocating out of position and operation when the web or package is advanced, or when the package advances, reciprocating with and operating on the package as it moves and then returning to the beginning of its stroke range while the web or package is stationary to operate on the following package.
The continuous web fed machines may have one or more reciprocating means which reciprocate while the web continues to advance or opposing endlessly rotating means such as wheels or endless linked belts containing a plurality of identical means for sequentially operating on the web as the web advances at a substantially uniform speed. The present invention relates to an improvement in continuous web fed type machines, and is designed to have a production rate substantially higher than that of presently known machines.
The primary problem with the aforementioned forming, filling, and sealing machines is that they are limited in the machine speed and web control required to continuously or intermittently make aseptic packages at a rate of speed higher than presently obtainable in an economically efficient manner.
The production rates of known blank fed designs and machines are limited by the time required to erect a blank into a carton, fill the carton, and seal it closed.
Intermittent and continuous continuous web fed machines are limited by the rate at which the web can be formed into a longitudinally advancing tube and the sealing mechanisms can transversely clamp, seal, and sever the tube into packages, of by the speed of the endlessly advancing linked chains or belts or rotating wheels on which the sealing mechanisms are mounted, or by the rate of reciprocating action of the sealing means used to form each package.
Increasing the speed of machines having a plurality of sealing mechanisms on a wheel or endless belts can cause the opposing wheels or belts to oscillate or bounce as the sealing mechanisms come in contact with each other to clamp and seal the package. This increases wear and decreases the useful life of the sealing mechanisms and could cause the wheels or belts to vibrate or become misaligned or untracked so that the sealing mechanisms would not seal accurately.
Similarly, merely increasing the frequency of reciprocation of the sealing means or other elements to increase the rate of production would also increase the wear and exaggerate any imbalance which could cause such an apparatus to shake itself apart. Adding a second reciprocating device, e.g., a sealing head, to increase the rate has been applied with some success, see, for example, Model AB-9 manufactured by Tetra-Pak. However, this technique also suffers from having a limited maximum reciprocation and production rates and adds undue mechanical complexity to permit the plural means to reciprocate past each other without interference.
Adding a second or multiple production lines does not solve the problem of increasing the production rate of a single machine. Multiple production lines mounted on a single frame may achieve some efficiencies in sharing common elements, but it is effectively the same as two or multiple machines. The rate of production is not increased, only the volume. Such machines, e.g., the aforementioned Combiblok machine which has two parallel production lines, and other known models which have four production lines, are unduly bulky, mechanically complicated, and occupy a substantial amount of floor space. Further, the more common elements shared by the multiple lines, the more complicated and expensive the machine becomes, especially if the entire machine must be stopped to fix a problem present in only one of the lines.
It is therefore an object of this invention to provide an improved longitudinal and transverse sealing method and apparatus for use in forming, filling, and severing polyfoil packages from a supply of polyfoil web at high rates of speed. It is also an object to provide such a method and apparatus for package forming under aseptic conditions.
It is another object to provide a circuit means to control the sealing operation of the machine to maintain continuous production of aseptic packages at a pre-selected fixed rate, which may be a variably controllable rate.
It is another object to provide a single relatively slowly rotating structure having a plurality of sealing mechanisms to maintain the web transversely clamped for a period of time sufficient to form hermetic seals without over stressing the mechanical limitations of the apparatus at high rates of production.
It is another object to provide an improved method and apparatus for controlling the application of radio-frequency energy for use in inductively sealing the polyfoil web to form aseptic packages.
It is a further object to use a secondary vertical induction heating coil, a transverse secondary coil mounted in each sealing mechanism, and a single induction generator to alternately form the longitudinal seal and spaced apart transverse seals in the tube to form filled sealed packages, and to adjust the power of the generator and energization of the vertical and transverse coils to control formation of the seals.